Inflators of various designs and configurations have been devised for use with air bag modules that are mounted in vehicles. Upon activation of the inflator, inflation gases are generated for pressurizing or filling the air bag. Inflators can be generally categorized in different groups or types. A hybrid inflator includes stored pressurized gas that acts with gases generated by a combustible propellant to generate inflation gases for filling the air bag. A pure or all pyrotechnic ("pyro") inflator refers to an inflator in which substantially entirely all of the gases for filling the air bag are propellant gases generated by a solid gas-generating propellant composition. There is no need to store a pressurized gas and the inflator is substantially free of a stored, pressurized gas.
It is also known to incorporate more than one inflator in an inflator system. That is, multiple including dual inflator systems have previously been advanced. Multiple inflators have particular application in inflator systems that operate differently, depending upon whether or not the collision involving the vehicle having the inflator system is characterized as a high impact or low impact vehicle collision. In that regard, the air bag of such an inflator system is designed to inflate when a threshold impact to the vehicle occurs or is exceeded. Different vehicle impacts can occur. According to one set of criteria or definitions, vehicle collisions can be characterized as being low impact or high impact. A low impact collision typically occurs when the impacted vehicle is traveling at a relatively low rate of speed. Relatedly, a low impact collision can occur when an impacting vehicle is traveling at a relatively low rate of speed when it strikes the impacted vehicle. Conversely, a high impact collision is commonly characterized by one or both of an impacted and impacting vehicle traveling at a relatively high rate of speed. The pressure developed in the air bag need not be the same for the low and high impact collisions. When a high impact collision occurs, it is desirable to inflate the air bag to a relatively high pressure while, with a low impact collision, it is desirable to inflate the air bag to a lesser pressure. Relatedly, depending upon the age and/or size of the vehicle occupant, it may be advantageous to control the pressure applied by the air bag. For young or small children, it is usually desirable to utilize less pressure in the air bag than when the vehicle occupant is an adult or a larger sized individual.
Inflation systems have been described that are intended to take into consideration such factors as the degree of vehicle impact, age and/or size of the vehicle occupant and/or the position of the occupant in the vehicle. In one prior art system, multiple gas generating units for filling an air bag with gas can be selectively activated. More than one such unit is activated when it is desirable to provide relatively increased pressure in the air bag. In another known prior art system, an electrically controlled vent valve, together with two igniters, are used. The vent valve provides a pathway for gases different from the pathway to inflate the air bag. Based on this configuration, if the electronic controller maintains the vent valve closed and fires each of the two igniter, the air bag inflates with 100% of the gas that is generated. On the other hand, for example, if the vent valve is controlled open and only one of the two igniter is fired, the air bag is inflated with a fraction of the maximum possible gas that could be provided.
Although the prior art describes systems and designs involved with controlling the inflation of an air bag, it would be beneficial to incorporate a relatively less complex arrangement that satisfies the key requirements associated with controlling the inflation of an air bag, including relying on components that are already available or are used in such a system, making as few modifications as is necessary to the air bag module and keeping the addition of parts thereto as few as possible.